Methane Clathrate Harvesting Systems and Methods

ABSTRACT

In some embodiments, a system may include a harvesting unit configured to operate under water to traverse and extract gas from clathrate hydrate deposits. The harvesting unit can include a housing defining an enclosure at least partially open along a bottom portion to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits. The harvesting unit may further include a separator chamber within the housing defining a negative pressure and configured to receive the clathrate slurry and a skirt coupled to the enclosure adjacent to the bottom portion and configured to form a flexible barrier between the enclosure and an external environment. The skirt may be formed from a plurality of elements configured to allow fluid flow therethrough.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present disclosure is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 13/051,919 filed on Mar. 18, 2011 and entitled “Systems and Methods for Harvesting Natural Gas from Underwater Clathrate Hydrate Deposits,” which is incorporated herein by reference in its entirety.

FIELD

The present disclosure is generally related to methane clathrate harvesting, and more particularly, to systems that may include propulsion, extraction, separation, delivery, and control systems integrated within a movable undersea device.

BACKGROUND

Methane clathrate (also called “methane hydrate,” “hydromethane,” “methane ice” or “fire ice”) comprises a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Within methane clathrate deposits, methane molecules are trapped inside “cages” of hydrogen-bonded water molecules. In other words, clathrate hydrates are clathrate compounds in which the host molecule is water and the guest molecule is typically a gas. Since the trapped molecules do not bond to the lattice, the clathrate hydrates are not chemical compounds, and the formation and decomposition of clathrate hydrates are first-order phase transitions and not chemical reactions.

Methane clathrates form at under water depths of less than 2000 meters, for example, adjacent to polar continental sedimentary rocks where surface temperatures are 0° C. to 2° C. and in oceanic sediment at water depths greater than 300 m where the water temperature is around 2° C. In addition, deep lakes may host gas hydrates as well. Continental deposits have been located in Siberia and Alaska in sandstone and siltstone beds at less than 800 m depth. Further, oceanic deposits seem to be widespread in the continental shelf and can occur within the sediments at depth or close to the sediment-water interface. Additionally, methane clathrate deposits may cap even larger deposits of gaseous methane.

Methane hydrates sometimes form from methane gas released as byproduct of deep sea drilling or from release of methane gas along oceanic geological faults. In some regions (e.g., the Gulf of Mexico), methane in clathrates may be at least partially derived from thermal degradation of organic matter. When released, the methane gas floats upward toward the surface of the water. In warm waters, the methane gas may be released into the atmosphere. In colder climates and at deep sea levels or in deep lakes, at least a portion of the methane gas may crystallize on contact with cold water. The crystallized methane gas can flow with deep water currents, eventually settling in deposits. Such deposits often exist in the ocean near the continental shelves.

The worldwide amounts of methane bound in clathrate hydrates is conservatively estimated to total twice the amount of methane to be found in all known fossil fuels on Earth. Testing of such deposits indicates that the average methane clathrate hydrate composition includes one mole of methane for every 5.75 moles of water. The average observed density has been around 0.9 grams per cubic centimeter. Based on these averages, a typical liter of methane clathrate solid would contain approximately 168 liters of methane gas (at STP).

SUMMARY

In some embodiments, a methane harvesting system may include a mobile trawler configured to move under water and to break up a selected portion of a methane clathrate deposit in deep water to form a slurry, a separation system configured to separate gas from the slurry, and a conduit configured to deliver the gas to a vessel at a surface of the water. The mobile trawler may include a skirt configured to encircle a base portion of the trawler and including openings to prevent a vacuum from forming in conjunction with an undersea surface.

In some embodiments, a system may include a harvesting unit configured to operate under water to traverse and extract gas from clathrate hydrate deposits. The harvesting unit can include a housing defining an enclosure at least partially open along a bottom portion to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits. The harvesting unit may further include a separator chamber within the housing defining a negative pressure and configured to receive the clathrate slurry and a skirt coupled to the enclosure adjacent to the bottom portion and configured to form a flexible barrier between the enclosure and an external environment. The skirt may be formed from a plurality of elements configured to allow fluid flow therethrough.

In some embodiments, a system may include a mobile harvesting unit configured to operate under water to traverse and extract gas from a clathrate hydrate deposit. The mobile harvesting unit can include a housing defining an enclosure and a propulsion system coupled to the housing. The mobile harvesting unit may also include a separator chamber within the housing and configured to apply a negative pressure. The separator chamber may be configured to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits. The separator chamber may include at least one of a centrifuge component and an impeller configured to separate gas from the pieces of the clathrate slurry and to dispel debris away from the harvesting unit. The mobile harvesting unit may further include a skirt coupled to the housing and configured to form a flexible barrier between the enclosure and an external environment along a bottom portion of the housing. In some embodiments, the mobile harvesting unit may include a method of breaking up the hydrates, such as a tiller or harrow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of a system configured to harvest methane clathrate from undersea deposits, in accordance with certain embodiments of the present disclosure.

FIG. 2 depicts a perspective view of the mobile clathrate hydrate harvesting unit of FIG. 1 configured to harvest methane clathrate from undersea deposits, in accordance with certain embodiments of the present disclosure.

FIG. 3 depicts a block diagram of a mobile clathrate hydrate harvesting unit of FIGS. 1 and 2, in accordance with certain embodiments of the present disclosure.

FIG. 4 depicts a block diagram of components of a slurry separator of the mobile clathrate hydrate harvesting unit of FIGS. 1-3, in accordance with certain embodiments of the present disclosure.

FIG. 5 depicts a diagram of components of a slurry separator of the mobile clathrate hydrate harvesting unit of FIGS. 1-4, in accordance with certain embodiments of the present disclosure.

FIGS. 6A-6C depict examples of different types of openings of the slurry separator of FIGS. 4 and 5, in accordance with certain embodiments of the present disclosure.

FIG. 7A depicts a gas separating portion of an embodiment of a slurry separator of FIGS. 4 and 5, in accordance with certain embodiments of the present disclosure.

FIG. 7B depicts a gas separating opening and a solid separating opening of the slurry separator of FIGS. 4, 5, and 7A, in accordance with certain embodiments of the present disclosure.

FIG. 8 depicts a portion of the mobile clathrate hydrate harvesting unit of FIGS. 1-3 and including a plurality of sensors, in accordance with certain embodiments of the present disclosure.

In the following discussion, the same reference numbers are used in the various embodiments to indicate the same or similar elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

While it is estimated that sedimentary methane hydrate reservoir probably contains two to ten times the currently known reserves of conventional natural gas, little has been done to harvest these deposits. A number of factors may contribute to the lack of progress. First, it has traditionally been difficult to locate substantial methane clathrate deposits, because they are deep under water. Second, traditional extraction technologies are too expensive to economically harvest methane from clathrate deposits that may be distributed across large areas of the sea floor. Such methane clathrate deposits can be detected, for example, using a “Bottom Simulating Reflector” (BSR), which produces a seismic reflection of the sediment-to-clathrate stability zone interface. Unequal densities of normal sediments and those laced with clathrates produce seismic reflections making detection of the methane clathrate deposits possible.

Embodiments of systems and methods for methane clathrate extraction are described below, which utilize a mobile harvesting unit together with mobile methane processing, storage, and distribution systems. Upon detection of the methane clathrate deposit, a mobile harvesting unit may be deployed that can be configured to traverse the ocean floor (using wheels, continuous tracks, actuating feet, or any combination thereof). The mobile harvesting unit may include a plow and optionally one or more rotating brushes to displace sediment to expose the clathrate deposit. Additionally, the mobile harvesting unit may include one or more elements (such as a harrow, a high pressure fluid spray, other types of blades, or any combination thereof) configured to break at least a portion of the clathrate into pieces to form a slurry. The mobile harvesting unit may have a slight vacuum or negative pressure (as compared to surroundings) to capture (draw) the slurry into the separator conduit and to direct escaping methane hydrate gas toward a collection vessel at the surface. The system may further include one or more separator units coupled to at least one of the mobile harvesting unit and the conduit to further break up solid clathrate within the slurry to release the trapped methane gas and to discard debris.

In some embodiments, the mobile harvesting unit may be controlled to move along a surface, such as a ledge or underwater surface in the ocean. The unit may be propelled by tracks, wheels, a fluid propulsion device, or any combination thereof. Moreover, the unit may be controlled to harvest clathrate hydrate from the surface according to a pattern selected to prevent slumping or collapse of the deposit.

In some embodiments, the system may further include a storage tanker at a surface of the ocean, for example, that is coupled to the conduit and configured to process the methane gas into a pressurized storage tank. The storage tanker may further include one or more distribution mechanisms configurable to couple to delivery tankers, which may load methane gas from the storage tanker and deliver the methane gas to a destination. An example of one possible embodiment of such a system is described below with respect to FIG. 1.

FIG. 1 depicts a block diagram of a system 100 configured to harvest methane clathrate from undersea deposits, in accordance with certain embodiments of the present disclosure. The system 100 may include a clathrate hydrate harvesting unit 102 under water that is communicatively and mechanically coupled to a ship 104 by a conduit assembly 162. The ship 104 may be floating on the surface 106 of the water 108.

In some embodiments, the conduit assembly 162 can include a fluid conduit including a plurality of segments, each having a substantially flexible portion. The substantially flexible portion may include substantially concentric inner and outer sidewalls and an adjustable pressure device configured to vary an internal annular pressure of the substantially flexible segment to counteract external pressure from a surrounding environment. Further, the conduit assembly 162 may include integrated wiring or channels to secure cables or wires to facilitate communication with the clathrate hydrate harvesting unit 102. One possible example of a conduit assembly 162 is described in U.S. Pat. No. 9,482,060 entitled “Adjustable Conduit”, which is incorporated herein by reference.

The ship 104 may include a processing system 110 configured to receive gas from the clathrate hydrate harvesting unit 102, to process the gas into a compressed state, and to provide the compressed gas to one or more storage tanks 112. The ship may further include a control system 114 configured to send signals to and receive signals from the clathrate hydrate harvesting unit 102. The control system 114 may also be coupled to a power generator 116 and to a gas distribution system 118, which may be coupled to one or more methane delivery systems 120 (such as a tanker, an on-shore tank, and so on).

The clathrate hydrate harvesting unit 102 may include a plow 122 configured to shift surface debris 133 away from a clathrate hydrate layer 132, which may be formed on top of an underlying surface 130. The plow 122 may be configured to push sediment and other surface debris 133 to either side of the harvesting unit 102. Further, the harvesting unit 102 may include one or more brushes 124 configured to sweep debris and sediment away from the clathrate layer 132. Additionally, the harvesting unit 102 can include one or more harrows 126 or cutting devices configured to cut or chop the clathrate layer 132 into pieces forming a slurry. A propulsion mechanism, such as tracks 128 (or wheels, propellers, or other propulsion devices) may be controlled to move the harvesting unit 102 along the clathrate layer 132, allowing the harvesting unit 102 to chop the clathrate layer 132 according to a pattern to release and recover the trapped methane gas.

The harvesting unit 102 may include a flexible skirt 134 or flap configured to encircle a base portion of the harvesting unit 102 to prevent debris and silt from moving under the harvesting unit 102 after the plow 122 has displaced it. In some embodiments, the skirt 134 may be formed from a plurality of flaps or bristles (similar to a broom), which allows water to flow through the skirt 134 while partially inhibiting particle and fluid flow. In some embodiments, the skirt 134 may be formed from a heavy rubber material, such as a mud flap from a long-haul truck. The skirt 134 may be formed from a plurality of such flaps, partially overlapping, to form a flexible barrier or shield that deters debris from shifting under the harvesting unit 102 and that helps to direct the flow of the gas toward the conduit assembly 162. By utilizing flaps or bristles instead of a solid barrier, a vacuum or negative pressure may be used to facilitate flow of the clathrate slurry into the separator chamber 150 without concern that the high water pressure of the surrounding environment and the vacuum or negative pressure might cooperate to create a suction between the harvesting unit 102 and the surface 130, which might inhibit movement of the harvesting unit 102. Further, the skirt 134 may be configured to assist in maintaining the flow of the clathrate slurry (formed by the harrows 126) within the periphery of the harvesting unit 102, directing the slurry toward the separator chamber 150.

The harvesting unit 102 may include one or more input/output (I/O) interfaces configured to receive signals from a control system 114 of the ship 104. The harvesting unit 102 may further include a controller 138 coupled to the I/O interfaces 136. The controller 138 may include one or more processing circuits, which may be programmable via signals from the ship 102 and which may execute instructions stored locally in a memory (not shown). Additionally, the harvesting unit 102 may include a plurality of sensors 140 and one or more lights 142 coupled to the controller 138 through the I/O interfaces 136. The sensors 140 can include gas sensors, optical sensors, spectral sensors, thermal sensors, RF frequency sensors, ultrasonic sensors, microwave sensors, sonar sensors, incline sensors, motion sensors, directional sensors, altitude/depth sensors, pressure sensors, rotation sensors, vacuum sensors, flow sensors, other sensors, or any combination thereof.

The harvesting unit 102 may further include a motor 144 coupled to the controller 138 and configured to provide motive power to the propulsion system (e.g., the tracks 128) and to provide power to a separator 152, a pump 146, and optionally a high pressure (HP) sprayer 148. The HP sprayer 148 may be configured to direct water jets toward the clathrate hydrate layer 132 in front of or behind the one or more harrows 126 to further cut or chop the clathrate hydrate to form the slurry to release and capture the trapped methane gas. In some embodiments, the water jets may be heated to facilitate conversion of the clathrate hydrate layer 132 into a slurry. The pump 146 may be controlled to selectively apply a pressure to the separator chamber 150, such as to provide a negative pressure. In the event that the negative pressure combines with external pressures to lock the harvesting unit 102 to the ground, the pump 146 may be reversed to alter the pressure to assist in releasing the pressure and moving the harvesting unit 102.

In some embodiments, the motor 144 may include a direct drive electric motor responsive to signals from the controller 138 to rotate a shaft, which may be used for motive power, to drive the pump 146, and to turn a propeller, blender, or centrifuge component of the separator.

The separator chamber 150 may include the separator 152 configured to break up the clathrate slurry to separate the trapped gas from the ice and other debris within the slurry. The separator 152 may include a centrifuge, pumps, filters, mixers, heaters, other components, or any combination thereof, which can cooperate to separate methane gas from the slurry. The separator 152 may be configured to dispel water, ice and debris, allowing the methane gas to proceed to the ship 104 through conduit assembly 162. The separator chamber 150 may further include a debris outlet 158 through which rocks, ice, and other debris may be discarded away from the harvesting unit 110. A quick connector 154 may couple the separator chamber 150 to the conduit assembly 162.

The conduit assembly 162 may include a gas conduit 156 configured to direct methane gas separated from the clathrate hydrate slurry toward the ship 104. The conduit assembly 162 may further include one or more channels configured to secure a plurality of cables and wires, which may carry power and control signals from the ship 104 to the harvesting unit 102 and to carry data and other signals from the harvesting unit 102 to the ship 104. The conduit assembly 162 may be formed from any material suitable for use in deep water. In some instances, conduit assembly 162 may be formed from a plurality of conduit sections formed from a plurality of segments of a substantially flexible tubing material. The conduit sections may include hoops or rings at each junction and optionally periodically along its length to allow for negative pressure while preventing the gas conduit 156 from collapsing under pressure from the water.

In operation, the harvesting unit 102 may be lowered to the undersea surface onto or adjacent to a detected deposit of clathrate hydrate. The harvesting unit 102 may be controlled to traverse the deposit, scraping and brushing silt and debris away from the clathrate hydrate deposit using the plow 122 and brushes 124, breaking up the clathrate hydrate using the harrows 126 and the high pressure sprayer 148 to form a slurry, drawing the clathrate hydrate slurry into the separator chamber 150 using a negative pressure provided by the pump 146, separating the gas from the clathrate slurry using the separator 152, and delivering the gas to the ship 104 via the gas conduit 156 of the conduit assembly 162. In some embodiments, the mobile harvesting unit 102 may include one or more gas sensors configured to detect concentrations of methane. In response to detecting a high concentration of methane, the mobile harvesting unit 102 may slow its forward progress to facilitate recovery of as much methane as possible. Further, the harvesting unit 102 may receive control signals from the ship 104 and may send data to the ship 104 through cables and wires 160 associated with the conduit assembly 162. In an example, the harvesting unit 104 may notify the ship 104 of the high concentration of methane gas and of the corresponding change to its forward velocity. Other embodiments are also possible.

In some embodiments, the speed of the harvesting unit 102, in terms of forward velocity, may be adjusted according to the concentration of methane gas. Further, the speed of the harrows 126, the high pressure sprayer 148, and the separator 152 may be adjusted to meet demand based on the volume of clathrate slurry. Other embodiments are also possible.

In one possible embodiment, as the storage tanks 112 of the ship 104 are filled, the ship 104 may control the harvesting unit 102 to stop producing gas, temporarily. Tanker vessels may couple to the ship 104 to receive the methane gas and to carry the methane gas to a port for delivery to a refining system. Alternatively, the ship 104 may disconnect from the harvesting unit 102 (or withdraw the harvesting unit 102 from the ocean floor). In a particular embodiment, the ship 104 may disconnect from the harvesting unit 102, leaving the harvesting unit 102 at the clathrate deposit site, and may proceed to a port to offload the gas to the refining system. A connection device at the surface 106 may include a floatation element to maintain the conduit at or near the surface 106 for ease of retrieval and reconnection, allowing a next ship 104 to couple to the harvesting unit 104 to continue the harvesting process.

In the event of a storm, the ship 104 may disconnect from the harvesting unit 102, leaving the harvesting unit 102 on the ocean floor so that the ship 104 may move out of the path of the storm. A floatation element, such as a buoy, may be coupled to the surface-end of the conduit assembly 162 to facilitate retrieval and reconnection once the storm has passed. Further, in some embodiments, the harvesting unit 102 may include a sonar or other transceiver, which may be part of the I/O interfaces 136 and which may be configured to generate a beacon signal or other signal through the water or through the conduit assembly 162 to an emitter at the surface-end of the conduit assembly 162. The beacon signal or other signal may be detectable by the ship 104 to facilitate location, reconnection, and/or retrieval of the harvesting unit 102. Other embodiments are also possible.

In an example, harvesting unit 102 may be controlled by systems within the ship 104 to traverse the underwater surface 133 and to carve or plow portions of the clathrate deposit 132, breaking ice cages to release trapped methane, and breaking the clathrate deposit 132 into small pieces that can be drawn into the separator chamber 150 as a slurry. Negative pressure applied to conduit assembly 162 by the ship 104 (and optionally by a pump associated with the separator chamber 150) draws the methane gas toward the ship 104. The slurry separator 152 can process the clathrate slurry to separate the methane gas from the ice and debris, releasing the methane, which rises to the surface 106 within the conduit assembly 152. The ship 104 may receive the methane gas and may pressurize the gas for storage. Further, the ship 104 also includes a mechanism for distributing the methane gas to transport vehicles for delivery to a destination.

In general, the mobile clathrate harvesting unit 102 enables recovery of significant undersea deposits of methane from clathrate hydrate deposits, at relatively low hardware costs. In particular, since the harvesting unit 102 is mobile and retrievable for re-use at different locations, the harvesting unit 102 may be used to recover methane from multiple deposits over its usable lifetime. In some embodiments, the body or housing of the harvesting unit 102 may be formed from a corrosion resistive material or may be coated with corrosion-resistive protective layers. In one particular embodiment, the frame of the harvesting unit may be formed from a composite material (e.g., carbon fiber with corrosion resistive coatings) to provide a relatively lightweight framework. The outer surface may be formed from the same or different materials and may be configured to define an enclosure to seal at least some of the components, such as the control electronics, the power electronics, the motor, and other elements from the water. The lightweight frame may facilitate retrieval and transportation of the harvesting unit 102 for repositioning and deployment to a clathrate deposit. Other embodiments are also possible.

It should be appreciated that, in the illustrated example, the skirt 134 is shown as being partially transparent, in order to show the brushes 124 and the harrows 126. Further, in the illustrated example, a portion of the propulsion system (e.g., the tracks 128) are shown as being outside of the skirt 134. In other embodiments (such as the embodiment shown in FIG. 2), the tracks 128 can be behind the skirt 134. Other embodiments are also possible.

In some embodiments, the pump 146 may be used selectively to aid the propulsion system. In an example, the pump 146 may be used to apply negative pressure to the separator chamber 150, which negative pressure may extend beneath the harvesting unit 102, pulling the harvesting unit 102 toward the clathrate hydrate deposit 132. However, the extra downward pressure supplied by the “vacuum” or negative pressure may reduce the efficiency of the propulsion system. To facilitate movement of the harvesting unit 102, the pump 146 may pulse or periodically reverse the pressure in the separation chamber 150 to dislodge chunks of debris and to lift or push the harvesting unit 102 away from the clathrate hydrate deposit 132 to reduce the pressure on the propulsion system. Other embodiments are also possible.

FIG. 2 depicts a perspective view 200 of the mobile clathrate hydrate harvesting unit 102 of FIG. 1 configured to harvest methane clathrate 132 from undersea deposits, in accordance with certain embodiments of the present disclosure. The harvesting unit 102 includes the plow 122 and the flexible skirt 134 behind the plow 122 and encircling a base portion of the harvesting unit 102. The plow 122 may displace debris 133 from a surface of the clathrate hydrate 132 to either side of the harvesting unit 102, forming a displaced pile 204 defining a path. Further, the tracks 128 may leave prints 206 in on the underlying surface as the harvesting unit 102 is moved.

The harvesting unit 102 may include a housing 202 with lights 142 and sensors 140. In the illustrated example, the lights 142 and sensors 140 are shown on a forward portion of the housing 202; however, the lights 142 and sensors 140 may be distributed across the housing 202. In some embodiments, the lights 142 and sensors 140 may include one or more actuators that can be used to redirect the lights 142 and sensors 140 in response to signals from the controller 138 of FIG. 1. The sensors 140 can include cameras or other optical sensors configured to capture video, images, or other optical data of the area around the harvesting unit 102.

The separator chamber 150 may be coupled to and may extend into the housing 202. The separator, generally indicated at 152, may be located within the separator chamber 150 and may be configured to spin or otherwise agitate the clathrate slurry to dispel debris through one or more debris outlets 158, which may include slots or openings in the side of the separator chamber 150. A quick connect coupling device 154 couples a conduit assembly 162 to the separator chamber 150 to receive the gas. The quick connect coupling device 154 may include a coupling used to provide a fast connection of fluid transfer lines, replacing threaded or flanged connections, allowing the connection to be established without wrenches.

While the debris outlets 158 are depicted as elongate openings, it should be appreciated that other shapes and other configurations of the debris outlets are also possible. Further, the separation chamber 150 may be located near a rear of the harvesting unit 102, so that the water and debris that were separated out of the clathrate slurry may be discarded away from the direction of operation of the harvesting unit 102. Other embodiments are also possible.

It should be understood that the example of FIG. 2 is provided for illustrative purposes only, and is not intended to be limiting. The harvesting unit 102 may be implemented with a different shape and profile. Further, in this example, the tracks 128 are behind the skirt 134. However, in other embodiments (such as in FIG. 1), the tracks 128 and/or other propulsion mechanisms may be external to the skirt 134. Other embodiments are also possible.

FIG. 3 depicts a block diagram 300 of the mobile clathrate hydrate harvesting unit 102 of FIGS. 1 and 2, in accordance with certain embodiments of the present disclosure. In the illustrated example, the harvesting unit 102 may include a clathrate slurry extraction system 304 coupled to a clathrate slurry separation system 306. The harvesting unit 102 may further include a propulsion system 308. Additionally, the harvesting unit 102 may include a control system 310, which may be coupled to the extraction system 304, the separation system 306, and the propulsion system 308.

The clathrate slurry extraction system 304 may include mechanical elements configured to expose, break or chop, and convert a clathrate hydrate deposit into a clathrate hydrate slurry of ice chunks, trapped and released gases, and debris. The extraction system 304 may include rotating or rotatable harrow blades 126 and optionally a high pressure sprayer 148, which may cooperate to cut the clathrate hydrate into chunks to form the slurry. The extraction system 304 may include a plow 122 and optionally rotating brushes 124, which may be configured to clear debris, silt, and other particles from a surface of the clathrate deposit. The extraction system 304 may also include a pump 324, which may be configured to provide pressurized fluid to the high pressure sprayer 148. Further, the extraction system 304 may include a controller 326, which may include one or more processing circuits and optionally a motor configured to control operation of the harrow blades 126 and the rotating brushes 124. The extraction system 304 may also include a flexible skirt 134 configured to keep the debris from moving under the harvesting unit 102.

In some embodiments, the controller 326 may be configured to monitor operation of the harrow blades 126 and the rotating brushes 124 using one or more of a plurality of distributed sensors 354 (which will be discussed in greater detail below). The controller 326 may also be configured to receive data from one or more sensors, including pressures, rotational sensors, motion sensors, temperature sensors, flow rate sensors, optical sensors, and so on. In one possible embodiment, the controller 326 may receive signals corresponding to a spectral analysis of the content of the, material content of the slurry (e.g., spectral analysis data), other data (including optical data), or any combination thereof.

The clathrate slurry separation system 306 may include a high pressure sprayer 330 coupled to a pump 146, which may be coupled to a controller 334. The separation system 306 may further include a slurry separator 152 including a screw pump or impeller 336 and debris outlets 158. In some embodiments, the high pressure sprayer 148, the high pressure sprayer 330, and the screw pump or impeller 336 may cooperate to further break up the chunks to separate gas from the clathrate slurry and to provide the gas to the conduit assembly 162 through the quick connector 154.

The controller 334 may be configured to monitor sensor signals from one or more of the distributed sensors 354 to determine parameters associated with the screw pump or impeller 336, the pump 146, the high pressure sprayer 330, and the debris outlets 158. If one or more of the signals indicate an operational parameter that is outside of an expected range, the controller 334 may be configured to selectively adjust operating parameters, such as by reversing or altering a speed of the operation of the pump 146 or the screw pump or impeller 336. Additionally, the controller 334 may be configured to communicate with other controllers, such as the controller 326, so that the clathrate slurry extraction system 304 may slow the creation and delivery of the clathrate slurry. If the debris outlets become clogged, the controller 334 may make other adjustments to mitigate the clog. Other embodiments are also possible.

The propulsion system 308 may include tracks 128, a steering system 346, wheels 348, and optionally an underwater propulsion system 342, which may include a propeller, a turbine, or other motion generating mechanism that can be controlled to move the harvesting unit 102. The propulsion system 308 may include a controller 340, which may include one or more processors, and which may be configured to send control signals to the steering system 346, the tracks 128, and the underwater propulsion system 342 to manage movement and steering of the harvesting unit 102.

The control system 310 may include one or more input/output (I/O) interfaces 136 that may be coupled to wires or cables of the conduit assembly 162 and that may include connectors to receive cable connections. Additionally, the I/O interfaces 136 may include one or more transceivers or other signal generators configured to send and receive data to and from other controllers, a control system on the ship 104, other devices, or any combination thereof.

The control system 310 may further include a controller 350 coupled to the I/O interfaces 136, to a plurality of distributed sensors 354, a plurality of sensors 140, lights 142, and a data log 360 configured to store information. The controller 350 may be configured to coordinate operation of the separation system 306, the slurry extraction system 308, and the propulsion system 308 to produce gas from underwater clathrate hydrate deposits and to provide the gas to the ship 104 through the conduit assembly 162.

It should be appreciated that the distributed sensors 354 may be provided within each of the subsystems and between subsystems. Further, each of the controllers 326, 334, 340, and 350 may utilize signal data from the distributed sensors 354 to determine operating parameters of the harvesting unit 102. Additionally, by distributing controllers 326, 334, 340, and 350 among the various subsystems, responsiveness of the controller to perturbations and detected events can be enhanced. In particular, rather than waiting for a control signal from a system on the ship 104, each subsystem can manage its own adjustments to small changes, improving responsiveness and enhancing the overall performance.

In some embodiments, each of the controllers 326, 334, and 340 may cooperate to enhance production of gas. The controller 350 may monitor production, store production related data in the data log 360, and may selectively communicate data to a control system on the ship 102. In a particular embodiment, the distributed sensors 354 may include a gas sensor configured to determine a concentration of methane gas being harvested. The controller 340 may alter one or more parameters of the propulsion system 308 to speed or slow the mobile harvesting unit 102 based on the concentration of methane gas, for example, to slow the unit 102 to collect more in an area of high concentration or to speed the unit 102 create more clathrate slurry in an area of relatively low concentration. Other embodiments are also possible.

FIG. 4 depicts a block diagram of components of a slurry separator 400 of the mobile clathrate hydrate harvesting unit of FIGS. 1-3, in accordance with certain embodiments of the present disclosure. The slurry separator 400 may be an embodiment of the separator 152 of FIGS. 1 and 2 and may be a part of the clathrate separation system 306 of FIG. 3.

The slurry separator 400 may include a controller 334 configured to receive control signals from the control system 310, from the ship 104, from other controllers, or any combination thereof. The controller 334 may be coupled to one or more centrifuges 402 (which may include a screw pump or impeller) configured to break up the clathrate slurry to release trapped gas. The controller 334 may also be coupled to one or more filters 404, a pump 406, a water exhaust system 408, and a particulate disposal system 410. In some embodiments, the controller 334 may be configured to receive sensor signals from one or more sensors associated with each of the components of the slurry separator 152 and to monitor and manage operation of the components to release gas from the clathrate slurry. Other embodiments are also possible.

The one or more centrifuges 402 may be coupled to filters 404, which may filter the debris from the composition. The filters 404 may be coupled to the pump 406 for pumping water and debris through a water exhaust system 408, which may be a pipe or tube for distributing the water back into the ocean away from the harvesting location. The pump 406 may also pump the debris through particulate disposal system 410 to dispel the debris and return it to the sea floor at a location that is preferably removed or at least behind and to the side of the harvesting unit 110. The filters 404 may also be coupled to the quick connector 154, which may be coupled to the gas portion of the conduit 156 to allow the natural gas that is freed from the clathrate slurry to continue through the conduit assembly 162.

In one possible embodiment, the slurry separator 152 may be included within the harvesting unit 102 between the harrow blades 126 and the quick connector 154. The slurry separator 152 may receive control signals and power from the cables 160 that are part of the conduit assembly 162. Additionally the slurry separator 152 may receive power from the cables 160. Further, the slurry separator 152 may receive control signals from the controller 334 and optionally from other controllers 326, 350, and 340 in FIG. 3.

In an alternative embodiment, grinding elements may be used in addition to or in lieu of centrifuges 402 to further break down the slurry into its component elements and to separate the natural gas from the clathrate slurry. Further, other processing means, such as heating, high pressure sprayers 330 (that can produce high pressure cutting water streams), impellers, heaters, other components, or any combination thereof may be used to facilitate the separation process. Other embodiments are also possible.

FIG. 5 depicts a diagram 500 of components of a slurry separator of the mobile clathrate hydrate harvesting unit 102 of FIGS. 1-4, in accordance with certain embodiments of the present disclosure. The diagram 500 includes a housing 502 that defines an enclosure sized to receive the separator chamber 150. The housing 502 may be contained within the housing 202 of the harvesting unit 102 (as depicted in FIG. 2) or may be part of the housing 202.

The diagram 500 depicts the harrow blades 126 adjacent to rollers 504, which may be configured to lift and advance the chunks of clathrate hydrate toward a heater 506. The heater 506 may include a heating element configured to at least partially melt the clathrate hydrate. The harrow blades 126, the rollers 504, and the heater 506 may cooperate to convey the clathrate hydrate to the separator chamber 150.

The separator chamber 150 may include a separator 152, which can include a screw pump or impeller 336. The screw pump or impeller 336 can be driven by a motor 508. The screw pump or impeller 336 can break up the clathrate hydrate, separating solids, which may be expelled through one or more channels 514. The released gas may rise through a low-pressure chamber 510 through a check valve 512 and through a quick connector 154 to the gas portion of the conduit 156.

FIGS. 6A-6C depict examples of different types of openings of the slurry separator 152 of FIGS. 1-5, in accordance with certain embodiments of the present disclosure. In some embodiments, the slurry separator 152 may include a housing or cover with a plurality of openings sized to allow gas to escape as the clathrate slurry is broken down.

In the example of FIG. 6A, a substrate 600 is shown that includes a plurality of small circular openings 602, which may be sized to allow gas to pass through and to prevent debris from passing through. The openings 602 may be distributed across the surface in an array. The distribution may include a uniform distribution. Alternatively, the openings 602 may be distributed in a non-uniform distribution. In some examples, the housing portion of the separator 152 may have a substantially conical shape, and the openings 602 may extend in a substantially linear arrangement radiating from a top of the conical shape toward the bottom of the conical shape, such that the openings 602 may be closer together near the top and spaced apart more toward the bottom.

In the example of FIG. 6B, a substrate 610 is shown that includes a plurality of substantially rectangular slots 612, which may be sized to allow gas to pass through and to prevent debris from passing through. The openings 612 may be distributed across the surface in an array, which may be uniform or which may have a non-uniform distribution. In some examples, the housing portion of the separator 152 may have a substantially conical shape, and the openings 612 may extend in a substantially linear arrangement radiating from a top of the conical shape toward the bottom of the conical shape, such that the openings 612 may be closer together near the top and spaced apart more toward the bottom.

In the example of FIG. 6C, a substrate 620 is shown that includes a plurality of slots 622. The slots 622 may have a rectangular shape, a parallelogram shape, an elliptical shape, or another shape. In some embodiments, the slots 622 can include an irregular shape. In this example, the slots 622 are arrayed diagonally across the substrate 620. In some examples, the housing portion of the separator 152 may have a substantially conical shape, and the openings 622 may extend in a substantially linear arrangement radiating from a top of the conical shape toward the bottom of the conical shape, such that the openings 622 may be closer together near the top and spaced apart more toward the bottom.

FIG. 7A depicts a gas separating portion 700 of an embodiment of a slurry separator 152 of FIGS. 1-6C, in accordance with certain embodiments of the present disclosure. The gas separating portion 700 includes a substrate 702 in a substantially conical configuration with a plurality openings 704 distributed across the substrate 702. In this example, the openings 702 may be small slits or slots configured to allow rising gas to escape while containing debris larger chunks of ice or small rocks that were trapped in the ice.

FIG. 7B depicts a portion of the substrate 702 including a gas separating opening 704 and a solid separating opening 706 of the slurry separator of FIGS. 1-7A, in accordance with certain embodiments of the present disclosure. In this example, the gas separating opening 704 may define a substantially vertical path for gas to escape. The solid separating opening 706 may be larger than the gas separating opening 704 and may define an angled path for particles to escape and fall. Other embodiments are also possible.

FIG. 8 depicts a portion 800 of the mobile clathrate hydrate harvesting unit 102 of FIGS. 1-5 and including a plurality of sensors, in accordance with certain embodiments of the present disclosure. The harvesting unit 102 may include a controller 350 configured to send and receive control signals to and from the ship 104, to and from other controllers, or any combination thereof.

The harvesting unit 102 may include a plurality of sensors 140 and a plurality of distributed sensors 354. In one embodiment, the sensors 140 may be associated with a control system 310 of the harvesting unit 102, while the distributed sensors 354 may be distributed across the propulsion system 308, the clathrate extraction system 304, and the clathrate separation system 306, as well as across the device as a whole.

The sensors 140 may include optical sensors 802 configured to capture image data associated with the surroundings of the harvesting unit 102, such as camera images or video. The controller 350 may send the image data to the ship 104 for analysis and to enable an operator on the ship 104 to view and control the operation and movement of the harvesting unit 102.

The sensors 140 may further include spectral sensors 804, which may be configured to provide spectral data to the controller 350. In some embodiments, the spectral sensors 804 may be configured to detect or track clathrate hydrate deposits based on a spectral signature. The sensors 140 may also include thermal sensors 806, which may provide temperature data to the controller 350. The thermal sensors 806 may be configured to detect radiant heat as well as measuring temperature associated with specific components.

The sensors 140 may also include radio frequency sensors 808, which may be configured to detect radio frequency (RF) signatures associated with various deposits and to provide signals related to the detected RF signatures to the controller 350. The sensors can include ultrasonic sensors 810, microwave sensors 812, and sonar sensors 814, which may be used to detect clathrate hydrate deposits under the sediment based on received signals.

The sensors 140 can also include one or more incline sensors 816, one or more motion sensors 818, and one or more directional sensors 820, which may provide incline, motion, and direction signals to the controller 350. These signals may be communicated to the ship 104 by the controller 350. Additionally, these signals may be used by the controller 350 to make immediate adjustments to the propulsion system 308, for example, to prevent the harvesting unit 102 from rolling over, for example, if the harvesting unit 102 is on a slope. Other embodiments are also possible.

The distributed sensors 354 may include gas sensors 822, flow sensors 824, pressure sensors 826, power sensors 828, blades sensors 830, vacuum sensors 832, temperature sensors 834, and rotation sensors 836. The distributed sensors 354 may be distributed throughout the harvesting unit 102 and may be associated with various components. For example, the blades sensors 830 can be associated with the harrow blades 126, the impeller blades 336, or any combination thereof. The rotation sensors 836 can be associated with the separator 152, the tracks 128, the pumps, and so on. The vacuum sensors 832 and pressure sensors 826 may be the same or may be calibrated for different types of pressure measurements. In an example, the vacuum sensors 832 may be configured to monitor negative pressure in the conduit assembly 162 as well as the negative pressure beneath the harvesting unit 102 and the negative pressure in the separating chamber 150. The pressure sensors 826 may monitor pressure in the pumps 146 and 324, in the sprayers 330 and 148, and so on. In some examples, the pressure sensors 826 may also monitor environmental pressure as well as pressure applied to the plow 122, the brushes 124, and so on.

The gas sensors 822 may monitor gas volume exiting the separator 152 or early detection of methane from the front of the unit behind the plow 122 and brushes 128. The flow sensors 824 may monitor water and clathrate slurry flow. The temperature sensors 834 may be configured to monitor temperature within chambers, such as the separation chamber 150 and the enclosure defined by the housing 202. Further, the temperature sensors 834 may measure environmental temperature as well as the temperature of various components, such as motors, pumps, centrifuges, and so on. If the temperature of a component is determined by the controller 350 to be out of an acceptable range, the controller 350 may automatically adjust one or more operating parameters of the component to avoid damaging the component. Other embodiments are also possible.

Additionally, the distributed sensors 354 may include one or more optical sensors 838 may be included within at least a portion of the clathrate extraction system 304, the clathrate separation system 306, the propulsion system 308, or any combination thereof. In an example, the optical sensors 838 may be included in the clathrate extraction system 304 and the clathrate separation system 306 to optically monitor the clathrate slurry to detect large particles, and so on. Other embodiments are also possible.

In conjunction with the systems, methods, and devices described above with respect to FIGS. 1-8, a clathrate harvesting system is described that may include a harvesting unit configured to move along an undersea surface. The harvesting unit may include a clathrate extraction system that can include a plow and optionally brushes to remove silt and debris from a clathrate hydrate deposit. The harvesting unit may also include one or more harrows or tillers and optionally a high pressure sprayer configured to break a clathrate hydrate deposit into pieces to form a slurry. A skirt may enclose a lower portion of the harvesting unit, which skirt may be formed from a plurality of flexible strips or elements, which can prevent silt and debris from flowing under the harvesting unit, while directing released gases into the separator chamber and while preventing a vacuum from forming between the harvesting unit and the ground.

In some embodiments, the harvesting unit may include a plurality of distributed controllers and distributed sensors, which can cooperate to monitor various parameters and to make adjustments based on the monitored parameters to protect components and optionally to optimize performance of the harvesting unit. For example, the motion of the harvesting unit, the speed of the harrow blades, and the power delivered to the separator may be adjusted dynamically to optimize release of the gas from the hydrate clathrate deposit, such as by speeding the cutting of the clathrate to increase the slurry flow rate, and increasing the speed of the separator to enhance the release of the gas. At the same time, the speed of travel may be reduced to allow the harvesting unit time to collect as much clathrate slurry as possible from a selected area, which may include a rich clathrate hydrate deposit. Other embodiments are also possible.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention. 

What is claimed is:
 1. A system comprising: a harvesting unit configured to operate under water to traverse and extract gas from clathrate hydrate deposits, the harvesting unit including: a housing defining an enclosure at least partially open along a bottom portion to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits; a separator chamber within the housing defining a negative pressure and configured to receive the clathrate slurry; and a skirt coupled to the enclosure adjacent to the bottom portion and configured to form a flexible barrier between the enclosure and an external environment, the skirt formed from a plurality of elements configured to allow fluid flow therethrough.
 2. The system of claim 1, wherein the skirt is formed from a plurality of rubber flaps at least partially overlapping.
 3. The system of claim 1, further comprising at least one of a plow and a brush to displace sediment from a selected one of the clathrate hydrate deposits.
 4. The system of claim 1, further comprising an extraction system configured to cut a portion of the selected one of the clathrate hydrate deposits to form a slurry.
 5. The system of claim 4, wherein the extraction system comprises: a plow configured to displace debris from the selected one of the clathrate hydrate deposits; a plurality of harrow blades configured to break the selected one of the clathrate hydrate deposits into pieces to form the clathrate slurry.
 6. The system of claim 5, further comprising at least one rotating brush configured to displace sediment from the selected one of the clathrate hydrate deposits.
 7. The system of claim 5, further comprising a high pressure sprayer configured to cooperate with the plurality of harrow blades to break the selected one of the clathrate hydrate deposits into the pieces to form the clathrate slurry.
 8. The system of claim 1, further comprising a control system including a plurality of distributed controllers, each controller including one or more processors associated with one or more components of the harvesting unit.
 9. The system of claim 1, further comprising a separation system within the separator chamber, the separation system configured to separate gas from the slurry, the separation system including at least one of a centrifuge component and an impeller configured to separate gas from the pieces of the clathrate slurry and to dispel debris away from the harvesting unit.
 10. A system comprising: a mobile harvesting unit configured to operate under water to traverse and extract gas from a clathrate hydrate deposit, the mobile harvesting unit including: a housing defining an enclosure; a propulsion system coupled to the housing; a separator chamber within the housing and configured to apply a negative pressure, the separator chamber configured to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits, the separator chamber including at least one of a centrifuge component and an impeller configured to separate gas from the pieces of the clathrate slurry and to dispel debris away from the harvesting unit; and a skirt coupled to the housing and configured to form a flexible barrier between the enclosure and an external environment along a bottom portion of the housing.
 11. The system of claim 10, wherein the skirt is formed from a plurality of elements configured to allow fluid flow therethrough.
 12. The system of claim 11, wherein the skirt is formed from one of a plurality of rubber flaps and a plurality of bristles at least partially overlapping to form a fluid permeable barrier.
 13. The system of claim 10, further comprising an extraction system configured to cut a portion of the clathrate hydrate deposit to form a slurry, the extraction system including: a plow configured to displace debris from the clathrate hydrate deposit; and at least one rotating brush configured to displace sediment from the clathrate hydrate deposit.
 14. The system of claim 13, wherein the extraction system further comprises: a plurality of harrow blades configured to break the clathrate hydrate deposit into pieces to form the clathrate slurry; and a high pressure sprayer configured to cooperate with the plurality of harrow blades to break the selected one of the clathrate hydrate deposits into the pieces to form the clathrate slurry.
 15. The system of claim 1, further comprising a control system including a plurality of distributed controllers, each controller including one or more processors associated with one or more components of the harvesting unit.
 16. A system comprising: a harvesting unit configured to operate under water to traverse and extract gas from clathrate hydrate deposits, the harvesting unit including: a housing defining an enclosure at least partially open along a bottom portion to receive a clathrate slurry associated with a selected one of the clathrate hydrate deposits; a skirt coupled to the enclosure adjacent to the bottom portion and configured to form a flexible barrier between the enclosure and an external environment, the skirt formed from a plurality of elements configured to allow fluid flow therethrough; a propulsion system coupled to the housing; a clathrate hydrate extraction system at least partially beneath the housing and configured to cut a portion of the selected one of the clathrate hydrate deposits to form a slurry; a clathrate hydrate separation system within the housing; and a control system including a plurality of distributed controllers, each controller including one or more processors associated with one or more components of each of the propulsion system, the clathrate hydrate extraction system, and the clathrate hydrate separation system.
 17. The system of claim 16, wherein the clathrate hydrate separation system comprises: a separator chamber within the housing defining a negative pressure and configured to receive the clathrate slurry; at least one of a centrifuge component and an impeller configured to separate gas from the pieces of the clathrate slurry and to dispel debris away from the harvesting unit.
 18. The system of claim 16, wherein the clathrate hydrate extraction system comprises: a plow configured to displace debris from the clathrate hydrate deposit; and at least one rotating brush configured to displace sediment from the clathrate hydrate deposit.
 19. The system of claim 18, wherein the clathrate hydrate extraction system further comprises: a plurality of harrow blades configured to break the clathrate hydrate deposit into pieces to form the clathrate slurry; and a high pressure sprayer configured to cooperate with the plurality of harrow blades to break the selected one of the clathrate hydrate deposits into the pieces to form the clathrate slurry.
 20. The system of claim 16, wherein the skirt is formed from a plurality of rubber flaps at least partially overlapping. 